Temperature compensated and self-calibrated current sensor using reference current

Abstract

A method is described to provide temperature compensation and self-calibration of a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. A reference electrical current carried by a conductor positioned within the sensing window of the current sensor is used to correct variations in the output signal due to temperature variations and aging.

1. A method to compensate for the temperature dependence of a current sensor comprised of a plurality of magnetic field sensors positioned around a first current carrying conductor, the outputs of which are electronically combined to produce a signal representing the current flowing in said first current carrying conductor, where a power source provides electrical power to each said magnetic field sensor, where the sensitivity to magnetic fields of each said magnetic field sensor is proportional to the voltage of the said power source that is applied to each said magnetic field sensor, comprising the steps of positioning a second current carrying conductor substantially parallel to said first current carrying conductor so that the plurality of said magnetic field sensors are positioned around said first and second current carrying conductors, passing a known alternating current in the said second current carrying conductor, electronically processing the said signal representing the current flowing in said first and second current carrying conductors to generate an error signal that depends only on the current in the said second current carrying conductor, and using the error signal to control the voltage of the said power source that provides electrical power to each of the said magnetic field sensors. 
   
   
     2. The method in  claim 1  where the signal processor is comprised of a synchronous electronic detector. 
   
   
     3. The method in  claim 1  where the magnetic field sensors are selected from the list including but not limited to Hall effect, magnetoresistive, giant magnetoresistive and magnetostrictive sensors. 
   
   
     4. A device for measuring electric current comprised of a plurality of magnetic field sensors positioned around a first current carrying conductor, the outputs of which are electronically combined to produce a signal representing the current flowing in said first current carrying conductor, where a power source provides electrical power to each said magnetic field sensor. where each said magnetic field sensor is sensitive to one vector component of the magnetic field generated by the electric current in said first current carrying conductor where the said magnetic field sensors are positioned along one or more continuous closed paths encircling the said first current carrying conductor, where the said magnetic field sensors have substantially identical sensitivity along each closed path, where the said magnetic field sensors are equally spaced along the length of each closed path, where the vector direction of sensitivity for each said magnetic field sensor is oriented to be tangential with the closed path at each said magnetic field sensor location, where the sensitivity to magnetic fields of each said magnetic field sensor is proportional to the voltage of the said power source that is applied to each said magnetic field sensor, where a second current carrying conductor is positioned substantially parallel to the said first current carrying conductor so that the plurality of said magnetic field sensors are positioned around said first and second current carrying conductors, Where a known alternating current is passed through said second current carrying conductor, where a signal processor generates an error signal from the said signal representing the current flowing in said first and second current carrying conductors to generate an error signal that is depends only on the current in the said second current carrying conductor, and where the said error signal controls the voltage of the said power source that provides electrical power to each of the said magnetic field sensors. 
   
   
     5. The device in  claim 4  where the signal processor is comprised of a synchronous electronic detector. 
   
   
     6. The device in  claim 4  where the magnetic field sensors are selected from the list including but not limited to Hall effect, magnetoresistive, giant magnetoresistive and magnetostrictive sensors.